Originally, a crankshaft drove the front end assembly drive (FEAD) system of an engine. The crankshaft was turned by the firing of pistons, which exerted a rhythmic torque on the crankshaft, rather than being continuous. This constant application and release of torque caused vacillations, which would stress the crankshaft to the point of failure. Stated another way, the crankshaft is like a plain torsion-bar, which has a mass and a torsional spring rate, that causes the crankshaft to have its own torsional resonant frequency. The torque peaks and valleys plus the inertia load from the acceleration of the reciprocating components causes the crankshaft itself to deflect (rotationally) forward and backward while it is operating. When those pulses are near the crankshaft resonant frequency, they would cause the crank to vibrate uncontrollably and eventually break. Accordingly, a torsional vibration damper (sometimes referred to as a crankshaft damper) is mounted on the crankshaft to solve this problem by counteracting torque to the crank negating the torque twisting amplitude placed upon the crankshaft by periodic firing impulses and to transfer rotational motion into the FEAD system, typically by driving an endless power transmission belt.
While existing torsional vibration dampers have been effective to extend the life of the crankshaft and to drive the FEAD system, changes in vehicle engine operation such as the introduction of start-stop systems to conserve fuel consumption add complexities to the system that the existing torsional vibration dampers are not designed to address. For instance, the start-stop system introduces impact forces due to belt starts that introduce the potential slip in the elastomer-metal interface in traditional torsion vibration dampers. Another concern is maintaining good axial and radial run-outs between the metallic components.
Some torsional vibration dampers also include an isolator system. Some of these isolator systems use a rubber spring for isolation as well as one for the vibration damper. Typically, these isolator springs are mold-bonded to another component of the torsional vibration damper. Mold-bonding adds expense to the manufacturing process by requiring special equipment and time to accomplish the molding process. Elimination of this step or requirement would be beneficial.
Traditional torsional vibration damper isolators have a rubber spring either in pure shear or in tension and compression. Both do not afford the stability that is required to hold the joint together axially and typically included a bearing system to protect the isolator spring from axial motion because isolator springs needed to have a soft torsional stiffness. Accordingly, improved designs for torsional vibration dampers that have a simpler configuration that do not include a bearing system, and also, preferably, do not involve mold-bonding of the isolator springs are desirable.